The present invention relates to a piezoelectric vibrator operating in a spreading vibration mode which is made of permanently elastic metal such as "Elimvar" metal.
A conventional piezoelectric vibrator of this type utilizes the spreading vibration of long or short sides of the piezoelectric element which is in the form of a rectangular plate and the like. One example of the conventional piezoelectric vibrator is as shown in FIG. 1. In FIG. 1, reference numeral 2 designates a spreading vibration mode piezoelectric element. The piezoelectric element 2 has a vibrating plate 5 of permanently elastic metal, a piezoelectric film 8, and a vibrating electrode film 9. The middles of the short sides of the rectangular vibrating plate 5 are supported through a pair of coupling pieces 6 and 6 by a holding frame 7. The piezoelectric element 2 is accommodated in a case (not shown) by supporting the holding frame 7 therein. The piezoelectric vibrator utilizes the spreading vibration of the short sides of the vibrating plate 5. That is, the vibration of the piezoelectric vibrator is in the direction of the short sides with a node of the vibration on the line connecting the coupling pieces 6 and 6. The frequency of the vibration relates to the length of the short sides.
In general, the above-described spreading vibration mode piezoelectric vibrator is scarcely employed as a piezoelectric vibrator using the permanently elastic metal, and instead it is mainly employed as a flexure vibration mode piezoelectric vibrator such as a tuning fork or piece which is operated at a relatively low frequency. These vibrators are obtained by cold-working a permanently elastic material into thin plates. In the cold rolling method, the material is rolled by a rolling machine having a high rolling factor. Therefore, during rolling, a phenomenon that the surface of the product which is in contact with the roller is roughened (a so-called "surface-roughening phenomenon") is cuased, or the scratches on the rolling roller affect the surface of the product; that is, the products manufactured are unsatisfactory in surface finish. Accordingly, although a flexure vibration mode vibrator relatively large in size causes no problem during operation, if, in a spreading vibration mode vibrator such as the above-described conventional one, the piezoelectric element 2 is miniaturized to about 1 mm.times.1 mm, then the roughness s (10 .mu.m usually) of the main surface 5a of the vibrating plate 5 cannot be disregarded. Furthermore, in the latter case, the products are fluctuated in the roughness s, and accordingly the vibrating plates 5 are not uniform in surface length and propagation speed. Accordingly, the characteristics such as for instance a resonance frequency characteristic are not sufficiently stable, with the results that the products are low in reliability, and it is not practical to miniaturize the vibrator so that it can be used for high frequency.